The present invention relates to a method and device for detecting misalignment in a motor vehicle radar system or a motor vehicle sensor system. Such methods and such devices are used, for example, within the framework of an automatic cruise control system of a vehicle for detecting preceding vehicles. A system of this type is also known as Adaptive Cruise Control (ACC). When installing the motor vehicle radar system in the motor vehicle, an exact procedure and a precise alignment of a central axis of the radiated electromagnetic waves to a central line of the motor vehicle in the longitudinal direction are performed.
U.S. Pat. No. 5,930,739 describes a method for measuring the yaw rate of a motor vehicle equipped with a LIDAR radar. In this method, the yaw rate ascertained by a yaw-rate sensor on the basis of the vehicle""s own velocity, a longitudinal distance to a fixed detection object, and the relative transverse velocity of the same fixed detection object in relation to the vehicle. The disadvantage of this method is that small offsets and far away detection objects are necessary for exact determination or correction. However, in radar applications, distant objects, in particular, are xe2x80x9cweak targets,xe2x80x9d which are difficult to measure, and whose position in the transverse direction to the vehicle in question cannot always be precisely determined due to the limited angular resolution of the radar system. For the same reason (limited angular resolution), the determination of transverse velocities of detected objects, in particular at greater distances, is also faulty.
German Patent No. 197 36 965 describes a method and an arrangement for testing the yaw rate of a moving object, in particular of a motor vehicle. In this context, the yaw rate is tested with the aid of objects that are located in the vehicle""s instantaneous environment. The objects detected by an environment sensor must be stationary objects. In this case, the actual position of the detected object is compared to a projection derived from the first measurement of the detected object as to the actual position. For this purpose, an object track is defined that includes all positions of the detected object at different, preselected times. In this context, the object track is formed starting from the determined position of the detected object, with the aid of the velocity and the yaw rate of the motor vehicle. The disadvantage of the method is that it is necessary to analyze the determined radial distance of the detected object to the motor vehicle in question into X and Y position coordinates. Typically, the angle of the detected object goes into such an analysis, the angle not being able to be determined in a particularly precise manner in the case of a system functioning on a laser or radar basis since a limited angle resolution must be used as a baseline.
German Published Patent Application No. 197 51 004 describes a method for processing radar signals, in which an instantaneous moving direction is determined by evaluating a plurality of object tracks formed for detected objects. In the event that this moving direction deviates from the alignment of the radar system, the object angles determined when detecting the objects within the framework of the angle resolution of the radar system are corrected by the determined deviation and related to the moving direction. The method relates to a trajectory analysis of the detected objects, the reflections of stationary objects being used in particular, since they form a particularly favorable foundation for determining the average moving direction.
An angular displacement determining device for determining the angular displacement of the radar central axis for use in a detection system for a motor vehicle is known from German Published Patent Application No. 198 33 065. In the case of this device, two situations are differentiated when determining the positions of the targets. The first case is that preceding vehicles are detected while the own vehicle travels straight. In this context, in the case of a correctly adjusted detection system, the result should be a distribution of the detected positions of the preceding vehicles that is parallel to the own travel direction. If this is not the case, a centroid is formed, a corresponding offset line is determined, and the detection system is accordingly corrected. The second case is that the own vehicle is cornering. In this case, an analysis of the relative velocity vectors between the own vehicle and the detected objects is performed. The disadvantage of this method is that the X and Y components of the relative velocity vector, which, as previously stated, cannot be determined in a particularly precise manner, are necessary for an analysis of the relative velocity vectors.
In comparison with the related art, the method according to the present invention is further refined in that, in the case of a method for detecting misalignment in a motor vehicle radar system, in which electromagnetic waves are emitted, electromagnetic waves reflected by a stationary object are received, and a relative angle (alpha_m) and a relative distance (d_m) or a longitudinal displacement and a transverse displacement between the detected object and a reference axis of the motor vehicle as well as a relative velocity (d_m_punkt) between the detected object and the motor vehicle are determined on the basis of the signals emitted and received, a correction value (alpha_null) is determined for relative angle (alpha_m) on the basis of relative angle (alpha_m), relative distance (d_m), and a velocity (v_F) of the vehicle in question or on the basis of the longitudinal displacement, the transverse displacement, and the vehicle""s own velocity (v_F). The method according to the present invention has the advantage that a correction value can be determined for the system itself from the measured values already present in a motor vehicle radar system. A quick and reliable correction of the measured angle value of the motor vehicle radar system is possible in this manner.
An advantageous further refinement of the method according to the present invention provides that a correction value (Psi_null_punkt) for yaw rate (Psi_m_punkt) is determined on the basis of relative angle (alpha_m), correction value (alpha_null), relative distance (d_m), relative velocity (d_m_punkt), the vehicle""s own velocity (v_F), and a yaw rate (Psi_m_punkt) supplied by a yaw-rate sensor. In other words: The measured yaw rate value supplied by any yaw-rate sensor can be corrected with the aid of the measured value supplied by the motor vehicle radar system. A reliable, quick determination of the yaw rate of the motor vehicle is possible in this manner.
In a particularly advantageous further refinement of the method according to the present invention, a yaw rate (Psi_punkt) of the motor vehicle is determined on the basis of relative angle (alpha_m), correction value (alpha_null), relative distance (d_m), relative velocity (d_m_punkt), and the vehicle""s own velocity (v_F). As a result of the method according to the present invention, it is possible with the aid of the data supplied by a motor vehicle radar system to quickly and reliably determine the yaw rate of the motor vehicle without a conventional yaw-rate sensor having to be present in the motor vehicle.
The great advantage of the method according to the present invention and of the device according to the present invention is that the offset determination of the measured angle value and the measured yaw rate value as well as the yaw rate determination can be carried out while the vehicle is in operation xe2x80x9conline.xe2x80x9d Thus, a shifting offset of the measured angle value and of the measured yaw rate value can be permanently and correctly compensated for even while the motor vehicle is in operation. It is not necessary to separately measure the sensors, e.g. in a workshop. In this context, the method according to the present invention is not based on an averaging of data ascertained by the motor vehicle radar system from stationary objects, but on a calculation having the data ascertained from the stationary objects as a basis. A further decided advantage is that the calculation can be performed in any driving situation, independently of whether the motor vehicle is moving in a straight line or is cornering.